JPS6021301A - Iron powder for compacted magnetic core - Google Patents

Abstract

PURPOSE:To obtain iron powder having a specified grain size and a specified density and giving magnetic core with high DC magnetic permeability and superior frequency characteristics by reducing iron oxide. CONSTITUTION:This iron powder for a compacted magnetic core has 50-270mum average grain size measured by sieve analysis and 2.8-3.5g/cm<2> apparent density, and it is manufactured by reducing iron oxide. The iron powder is compacted and hardened with resin or the like to form a starting material for a compacted magnetic core used as a reactor core, a noise filter core or the like. When the starting material is used, a compacted magnetic core with superior magnetic characteristics, especially frequency characteristics can be obtd. stably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to iron powder that is a raw material for powder magnetic cores used in reactor cores, noise filter cores, and the like.

As is well known, a powder magnetic core made by compacting iron powder and solidifying it with resin etc. has better frequency characteristics than normal totally magnetotropic materials, and has better temperature stability than ferrite. It has the advantages of high saturation magnetic flux density, small fluctuations in magnetic permeability with respect to applied magnetic field, and can be manufactured at low cost, so it is used for reactor cores, noise filter cores, etc.

By the way, the important properties of a powder magnetic core include high magnetic permeability to a DC magnetic field (DC magnetic permeability) and good frequency characteristics. Among these, the first point, DC magnetic permeability, is closely related to the density of the powder magnetic core, and can be achieved by compacting at high pressure or using iron powder with high purity and good compressibility. , it can be improved relatively simply. However, regarding the second point, that is, the influence of iron powder properties on frequency characteristics, which has not been fully elucidated, The reality is that powder is used as is in powder magnetic cores, and as a result, the frequency characteristics of conventional powder magnetic cores often do not always reach a satisfactory level.

This invention has been made in view of the above circumstances, and is based on the novel knowledge of the present author and others regarding the relationship between the frequency characteristics of a powder magnetic core and the properties of iron powder, to stably obtain good frequency characteristics. The purpose of this invention is to provide an iron powder different from ordinary iron powder for powder metallurgy.

Next, the findings of the present inventors, which formed the basis of this invention, will be explained.

As with general magnetic materials, as the operating frequency increases, the powder magnetic core's Pi permeability decreases relative to its DC permeability, and at the same time its loss increases, eventually making it unusable as a magnetic material. In the case of powder magnetic cores, it is the opinion of the present inventors that (
It is thought that 1) the insulation state between particles and (2) the particle size of the particles.

In other words, regarding (1), when the iron powder particles are pressed together and the insulation deteriorates, the apparent electrical resistance of the powder magnetic core decreases, making it easier for eddy currents to flow between the particles when an alternating magnetic field is applied. , the magnetic properties deteriorate.

On the other hand, regarding (2), even if the insulation between the particles is sufficient, if the iron powder particles are coarse, eddy currents tend to flow inside the particles and the magnetic properties deteriorate.

Therefore, from the viewpoint of (2), in order to maintain good frequency characteristics, it is desirable that the iron powder particles are not too coarse. However, if the iron powder is too fine, the compressibility of the iron powder will be extremely degraded, resulting in a decrease in DC permeability. Therefore, it is considered that the lower and upper limits of the particle size of the powder powder should be defined.

On the other hand, from the viewpoint of (1), it is desirable that the apparent density of the iron powder is high. That is, iron powder with a low apparent density has irregularly shaped particles, and therefore, when compacted, the contact area between the particles is large, and the insulation between the particles is likely to deteriorate. However, if the apparent density is too high,
As is well known, the strength of the powder molded product decreases, and even if it is hardened using a resin or the like, there is a risk that the molded product will be destroyed if it is not handled with great care immediately after molding, which is not preferable. Therefore, it is considered that lower and upper limits should be specified for the apparent density of iron powder.

In addition, from the above considerations, from the perspective of frequency characteristics, atomized iron powder produced by spraying molten iron with water is superior to reduced iron powder produced by reducing iron oxide. It seems like it is. This is because the apparent density of reduced iron powder is usually around 2.5 g/cm, whereas the apparent density of atomized iron powder is usually 3.0 g/cm.
This is because atomized iron powder has a higher apparent density than reduced iron powder. However, detailed experiments conducted by the present inventors have revealed that reduced iron powder actually has better frequency characteristics than atomized iron powder. This point will be shown later using experimental results, and the reason is thought to be as follows. In other words, even if the particle size according to sieve analysis is similar, reduced iron powder particles are spongy due to the manufacturing method, so compared to atomized iron powder, which has fewer pores within the particles, the reduced iron powder particles are actually smaller. In other words, since it has the effect of having a small particle size, it is difficult for eddy currents to flow within the particles, and good frequency characteristics can be obtained.

As mentioned above, 17 powder magnetic cores with excellent magnetic properties
In order to achieve this goal, it is necessary to focus on the particle size and apparent density of the iron powder used, as well as the iron powder properties caused by the iron powder manufacturing method. For one reason, ordinary iron powder for powder metallurgy was used in powder magnetic cores, and as a result, sufficient magnetic properties were not achieved.

Based on the above-mentioned knowledge, the present inventors carried out detailed experiments on the particle size and apparent density range of iron powder particles that should be specified, and as a result, the average particle size determined from sieve analysis was 50.
We discovered that reduced iron powder with an apparent density in the range of 2.8 to 3.5 o/cm is excellent as an iron powder for powder magnetic cores, and we came up with this invention. be.

Therefore, the iron powder for powder magnetic cores of the present invention is iron powder produced by reduction of iron oxide, has an average particle size determined by sieve analysis in the range of 50 to 270 particles, and has an apparent It is characterized by having a density within the range of 2.8 to 3.5 Q/G.

This invention will be explained in more detail below.

First, by sieve analysis. The reason why the upper limit of the average particle diameter was set at 270 tones will be explained. Figure 1 shows that the apparent density is 3
．． Using reduced iron powder and water atomized iron powder, which are approximately equal to 0 ± 0.1 g/C7 and have different average particle sizes,
A ring-shaped molded body with an outer diameter of 38'mm, an inner diameter of 25mm, and a height of 6.5mm was created by compacting with a pressure of t/ct, and the frequency dependence of magnetic permeability was measured using an impedance meter. , shows the result of finding the limit frequency. Here, the limit frequency is conveniently defined as the frequency at which the magnetic permeability becomes 80% of the DC magnetic permeability.

As is clear from No. 10, any iron powder with a small average particle size has a critical frequency of about 0.3 Ml-1z, but in the case of reduced iron powder, if the average particle size exceeds 270 tones, The limit frequency is as small as 0.2 MH2 or less, making it unsuitable for powder magnetic cores that require good frequency characteristics.

Therefore, the upper limit of the average particle size of reduced iron powder was set at 270 grains. Furthermore, from FIG. 1, it is clear that atomized iron powder has inferior frequency characteristics to reduced iron powder, and is therefore not suitable for applications requiring good frequency characteristics.

Next, the basis for setting the lower limit of the average diameter to 50JJI11 will be explained. FIG. 2 shows the results of measuring the DC magnetic permeability of a molded body made of the same reduced iron powder used in the measurement of FIG. 1. From FIG. 2, it is clear that the average particle size must be 50 pm or more in order to secure the minimum magnetic permeability of about 40 normally required for powder magnetic cores.

On the other hand, the reason why the lower limit of the apparent density was set at 2.8 MOIfi is as follows. Figure 3 shows that the average particle size is almost equal,
Look I! ) Mill-scale reduced iron powders with different densities were compacted into a ring shape in the same manner as above, and the results of determining the critical frequency are shown. From FIG. 3, it is clear that in order to ensure a critical frequency of 0.2 MHz or higher, the apparent density must be 2.8 g/cm or higher.

Furthermore, the reason why the upper limit of the apparent density was set at 3.5 a/c will be explained with reference to FIG. This figure 4 shows that the same reduced iron powder used in the measurement in figure 3 was used, 1% by weight of zinc stearate was added as a lubricant, and the powder was compacted at a pressure of 5 t/c♂. Size 35PIII+, width 10III1
11 This shows the results of creating a molded body with a height of 6FllI+ and measuring its transverse rupture strength, and the apparent density is 3.5Q.
/fJ', the bending resistance normally required for a molded product is 0. '5k (1/- is clearly not achieved. Therefore, the apparent density is 3.5 g/co1g
, it needs to fit below.

As mentioned above, the raw material iron powder is reduced iron powder such as mill scale reduced iron powder and has an average particle size of 50 to 27
It is clear that a powder magnetic core having excellent properties can be stably obtained only by using iron powder having an apparent density of 2.8 to 3.5 g/am.

Examples of this invention are described below.

Example 1 Mill scale 3 original iron powder with an average particle diameter of 78 mm and an apparent density of 2.93 (II/cm) was compacted at 2 t/c/, and had an outer diameter of 38 mm, an inner diameter of 25 mm, and a height of 6 mm. .5+!lII+
A ring-shaped molded body was prepared, and the frequency dependence of magnetic permeability was measured using an impedance meter. As a result, a DC permeability of 51 and a limit frequency of 0.29 MH7 were achieved.

Example 2 An experiment similar to Example 1 was conducted using mill scale reduced iron powder with an average particle size of 215 mm and an apparent density of 3.03 (J/C♂), and a DC permeability of 57 and a limit frequency of 0.28 MH2 were achieved. did.

Example 3 An experiment similar to Example 1 was conducted using mill scale reduced iron powder with an average particle size of 83 pHl and an apparent density of 3.22 g/c, and a DC permeability of 49 and a limit frequency of 0.38 MH2 were achieved.

As is clear from the above explanation, the iron powder for powder magnetic cores of the present invention is optimal as a raw material powder for powder magnetic cores used for reactor cores, noise filter cores, etc.
By using this, it is possible to stably obtain a powder magnetic core with excellent magnetic properties, especially frequency properties.

[Brief explanation of drawings]

Figure 1 is a correlation diagram showing the relationship between the average particle diameter of reduced iron powder and atomized iron powder and the critical frequency of a molded product using those iron powders, and Figure 2 is a correlation diagram showing the relationship between the average particle diameter of reduced iron powder and the limit frequency of a molded product using those iron powders. Figure 3 is a correlation diagram showing the relationship between the DC permeability of the iron powder compact used, and Figure 3 is a correlation diagram showing the relationship between the apparent density of reduced iron powder and the limiting frequency of the iron powder compact using it. , FIG. 4 is a correlation diagram showing the relationship between the apparent density of reduced iron powder and the bending force of an iron powder molded article using the same. Applicant Kawasaki Steel Co., Ltd. agent Patent attorney Yutaka 1) Takehisa (1 idiot) 1st ward average grain size (μm) Figure 2 Hitoshi Hitoshi (,pun) Figure 3''' ( Coconut L411 to ~ p degree ζμyoung

Claims (1)

[Claims] Iron powder produced by reduction of iron oxide, with an average particle size of 50 to 270 as determined by sieve analysis.
Within the voice range and with an apparent density of 2.8 to 3.5 M
An iron powder for pressurized magnetic cores characterized by being within the range of C♂.